Generally, blow-by gas is gas that leaks through a gap between a piston and a cylinder and flows into a crankcase. Blow-by gas contains non-combusted gas, combusted gas, and oil vapor. If blow-by gas remains inside a crankcase, pressure inside the crankcase increases. The increased pressure applies resistance to movement of the pistons and corrosion is likely to occur within the engine.
Therefore, to reduce blow-by gas from gathering within a crankcase, a technique for releasing blow-by gas is to recycle the blow-by gas and supply it to an intake device. A specific method of accomplishing this goal is to provide an oil drain hole and/or a blow-by hole on a crankcase to exhaust the blow-by gas to a cylinder head cover.
However, the blow-by gas recycle system does not smoothly pass the blow-by gas inside the crankcase to the cylinder head cover. Therefore, the pressure within the crankcase is maintained as a positive pressure. As a result, the reciprocating motion of the piston is interfered with so output is lowered. Furthermore, the force that pushes oil into the crankcase is exceeded by and oil leaks develop. Additionally, the oil contained in blow-by gas is supplied to a combustion chamber with the blow-by gas, thereby, increasing oil consumption and emitting harmful exhaust gas. Furthermore, carbon deposits increase within the engine and result in a lowering of the combustion efficiency.